Allergic reactions pose serious public health problems worldwide. Pollen allergy alone (allergic rhinitis or hay fever) affects about 10-15% of the population, and generates huge economic costs. For example, reports estimate that pollen allergy generated $1.8 billion of direct and indirect expenses in the United States in 1990 (Fact Sheet, National Institute of Allergy and Infectious Diseases; McMenamin, Annals of Allergy 73:35, 1994). Asthma, which can be triggered by exposure to antigens, is also a serious public health problem, and like anaphylactic allergic reactions, can lead to death in extreme cases. Asthma currently accounts for millions of visits yearly to hospitals and is increasing in frequency. The only treatment currently available is for alleviation of symptoms, for example, to relieve constriction of airways.
Perhaps even more serious than the economic costs associated with pollen and other inhaled allergens (e.g., molds, dust mites, animal danders) is the risk of an anaphylactic allergic reaction observed with certain allergens, such as food allergens, insect venoms, drugs, and latex.